The invention is generally directed toward filtering and purifying heated liquid media and is primarily directed toward filtering and purifying cooking oils used in deep fry cooking. The invention is more specifically directed toward providing a retrofit recirculating filter system which is a separate apparatus from the deep-frying equipment.
Deep fry cooking, especially in fast-food type restaurants, necessitates maintaining a large volume of fate or oils at high temperatures usually from about 250.degree. F. to 450.degree. F. The maintenance of the purity of these cooking media is a great concern to the restaurant owner as well as ultimately the consumer. When a cooking oil is not filtered or purified, its useful life can be limited to just one business day, and sometimes less. The useful, and healthful, life of a cooking oil medium is also affected by the type of food being cooked. Even with daily draining and straining through a cloth strainer, the cooking oil at best can be kept useful and healthy for no more than about two to four days even when cooking only a single type food. Standard size deep fryers used in commercial establishments will typically hold from about two to about six gallons of oil or shortening. In large establishments numerous deep fryers are used. With the cost of cooking oil at its present value, each fryer may hold up to about fifteen to thirty dollars worth of material. Accordingly, the replacement costs for these cooking oils can be a significant expense in fast-food outlets and restaurants. If the cooking fats or oils are not cared for properly, these repetitive expenses must be incurrd after the useful life of the oil has ended, which is usually a maximum of two to four days.
When foods are cooked by deep frying, a greater amount of the fat or oil is absorbed by the food when the cooking medium is contaminated with moisture, free fatty acids, and carbons. Contamination and the degradation of the cooking fat or oil commences as soon as it is heated and the first food to be cooked is placed into it. Degradation of the cooking oil continues at an accelerated pace as time elapses and as more food is cooked in it. The standard analysis for determining whether a cooking oil is suitable for further use involves measuring: (1) peroxide value, which is the progression toward rancidity (oxidation breakdown); and (2) the measurement of the free fatty acid which is a reading of the hydrolytic breakdown of the fat.
Degradation of the cooking oil is further advanced by the introduction of water from the foods being cooked therein and also from the solid residue left in the oil from seasonings, flavor enhancers, and particles of batter or breading that drop from the food items as they are being cooked.
The oxidation breakdown of fresh cooking oil or fat is about 1.0 units. When the oxidataion breakdown reaches 20.0 units, the fat or oil is rancid and should be changed. The hydrolytic breakdown of the fat in a fresh oil or fat, such as lard or shortening, is about 0.05 percent. When the hydrolytic breakdown reaches 2.0 percent, the oil or fat should be changed. The principal causes for the degradation of cooking oils or fats in deep fryers are therefore considered to be oxidation and the presence of free fatty acids. The continuous heating of the cooking oil, as well as the usual cooling off period overnight followed by reheating the next morning, contribute greatly to the oxidation process. The solid residue left from the food and batter accelerates the oxidation process toward rancidity. Also, the solid residue that remains in the cooking medium becomes scorched and results in the discoloration of the oil or fat and also tends to transfer odors and bad taste to other foods cooked in the medium. The cooking ability of contaminated and degraded oil is much less and becomes worse during further cooking since the breakdown causes greater amounts of the oil or fat to be cooked into the food placed therein.
Certain free fatty acids, such as palmitic, oleic, amino, and stearic, can also be driven from the foods being cooked and contribute to this degradation of the cooking oil and fat. Numerous compounds and agents have been used in the prior art treatment of cooking oils and fats, such as the use of potassium hydroxide, to reduce acidity. Also, activated bone char has been used to eliminate odors. Others have taken advantage of the hygroscopic and absorbent qualities of diatomaceous silica for use in filtering apparatus. Various screening device, cardboard and paper filter layers, and homogenizing disks have also been used in the past.
The prior art techniques offer a myriad of systems and apparatus that usually either require very elaborate and complicated installation necessitating constant maintenance and frequent service, or a system with limited application caused by an inability to be useful in a variety of different deep frying cooking systems or requiring a large amount of alteration and modification to in-place deep frying equipment. Certain portable systsms have been developed in the prior art but have met with limited acceptance in the industry.
The problems addressed by prior art filtering and purifying techniques focus on extending the useful life of the cooking medium and thus reducing the cost of replacing oils and fats. Some techniques employed in the prior art involve extending the useful life of the cooking medium by not overheating the oil or fat. Other non-mechanical filtering techniques involve the simple removal of solid residue left in the deep fryer on an ongoing basis during the day, such as pieces of food and batter that fall through the cooking basket often used for onion rings, french fries, and the like. Also, a daily draining procedure of the cooking medium from deep fat fryers has been used and thereafter the oil or fat is drained through a metal or cloth strainer.
One techique which will extend the life of a cooking oil or fat is to use a separate deep fat food fryer for each specific type of food to be cooked. This is not always possible in smaller establishments. A separate fryer system necessarily requires the heating of numerous independent volumes of cooking media which may be unevenly used and add further cost to the cooking procedure. Highly sophisticated apparatus have employed a series of disk-type screens or cylindrical filtering units housed in canisters. Either negative or positive pressure siphon systems have forced the cooking oil on a continuous basis through such filters to purify or clarify the oil.
It will be understood that the treatment of cooking media involves the full variety of cooking substances, used, such as shortening, lards, animal and vegetable fats and oils, collectively sometimes referred to herein as simply cooking oil or fat. It would be desirable for a filtering and purifying system to be applicable to all cooking media used in so-called deep fat frying. In view of the foregoing problems of degradation and contamination found with the utilization of deep fat frying media, it is a primary purpose of this invention to provide a highly effective, dependable, portable apparatus, preferably for retrofitting with existing frying systems, having substantially universal capability for filtering and purifying cooking oils used in deep fat frying.
It is further an object of the invention to provide a retrofit filtering and purifying apparatus usable with existing deep fat frying vessels without the necessity of modifying or altering present restaurant equipment.
A concomitant object of the invention is also to provide a system that is fully portable allowing the restaurant owner to move it from one site to another as needed or retrofit with existing frying systems.
A collateral object of the invention is to provide such a filtering system that can be housed above or below the deep fat fryer, or even alongside, in a semi-permanent design whereby it can be incorporated with a variety of existing cabinet arrangements at restaurant work stations.
An important object of this invention is to provide a suitable and efficient method and means for greatly extending the useful life of the cooking medium.
Another object of the invention is to provide a filtering apparatus and system that effectively filters fine food particles, fatty acids, carbons, oxidized matter, and residue down to about three microns in size.
Another important object of the invention is to provide a filtering system that also purifies the cooking oil by eliminating odors created by the foods cooked therein.
Another important object of this invention is to extend the useful life of the cooking medium without the need to replace or modify existing deep fat fryers that are presently in use. A particular advantage offered by this invention is the method and means whereby the retrofitting of this invention to an existing deep fat fryer can be accomplished by a layman, minimally experienced in the use and maintenance of deep fat fryers and the cooking medium used therein.
Another object of the invention is to provide a filtering system, method, and apparatus which purifies cooking oil on a recirculating and continuous basis whereby the taste from previously cooked food is not transferred to the next type of food cooked therein.
Furthermore, it is another goal of the invention to remove water that is introduced into the cooking oil without the use of a hygroscopic or other absorbent compound.
A related object of the invention is to achieve the filtering of cooling oil in the normal high temperature cooking temperature ranges of from about 250.degree. F. to about 450.degree. F.
Another objective of the invention is to have the capability to filter and purify cooking oil which may be of the solid type, such as lard, as well as the liquid type, such as vegetable oils.
Another object of the invention is to provide a simply maintained and efficient system requiring very little installation time and cost, or continuing supervision.
It is further an object of the invention to provide a filtering system for deep fat frying wherein a hardened shortening or lard medium is used whereby a portion of the apparatus may include heating means adapted to liquefy hardened shortening therein when the system is activated whereby to be almost immediately ready for use when required.
A further goal of the invention is to provide the combination with a timer control device for a retrofitted recirculating filter system, which control device may sequence the operation on a predetermined time schedule or which may be continuously set to run throughout the period in which the cooking oil in the deep fat fryer is used. The invention would also be desirably usable with a temperature or pressure sensitive control means for monotoring same to activate or de-activate the system at pre-set pressure or temperature values.
It is a further object of the invention to provide a recirculating filtering system for cooking oil that can extend the useful life of cooking oil in a fast-food type restaurant, thay may be open for a substantial portion of each day, up to about at least eight to ten days without requiring changing the oil. Additionally, it is a collateral object of the invention to provide such a system wherein the filtering medium used in the apparatus need only be changed once every week to ten days of operation, or at the same time that the oil is changed once a change interval is established for a particular deep frying system.
An additional related object of the invention is to provide a recirculating filtering system that is not limited to application for deep fryers using cooking oils but may be also used in the pharmaceutical and chemical industries for filtering and refining in various industrial and chemical procedures, liquids such as acetone, acid baths, washes and flushes, in order to remove impurities therefrom and whereby to be able to extend the longevity of the liquid for subsequent baths, washes and the like.
Accordingly, it is an object of the present invention to provide an improved filtering system for cooking oils to eliminate the contamination and degradation caued by oxidation breakdown that causes rancidity, and the hydrolytic breakdown, that causes free fatty acids to be deposited on the foods cooked. This invention provides a complete filtering system that removes solids to micron size and the free fatty acids caused by introduction of water from foods cooked therein.
The invention can be summmarized as providing a pump-driven siphon drawing means taking a liquid, for example, liquefied hot cooking oil, from the cooking vessel through a pickup and draw line to be introduced under pressure into the bottom of a filter canister containing a fiber filtering media and an overlying retainer padding. The filtering media being contained within the canister by a lid assembly means. An outlet port associated with the interior of the canister in a region defined by the lid assembly means in a space therein above the retainer pad whereby to receive, under pressure, oil forced upwardly through the filtering media. The outlet connects with a return line and, preferably, into a return tube extending interiorly of the cooking vessel for return of the filtered and purified oil.
In accordance with the present invention, cooking oil, normally at temperatures of from 250.degree. F. up to about 450.degree. F. is picked up from the cooking vessel and passed through the filter canister and circulated back into the cooking vessel clean of solid particles of down to at least about 3 micron size. Depending upon the individual requirements for filtering system, the filtering can be combined with a control timer for (1) continuous, (2) intermittent, or (3) timed cycling. By add-on devices to the filtering apparatus the system can be made automatic whereby (1) the amount of time for which the filter may be used may be monitored, (2) it can be set for start when suitable operating oil temperature is reached, (3) it may be set for shut-down when oil temperature falls below suitable operating temperature, or (4) it may be set to shut-down when back pressure is too high or if the siphon should draw air.
The system is intended to operate under a little back pressure and provide a capacity of from about 15 to 48 gallons per hour of filtering with pressure optimally in the range of from 5 to 35 p.s.i. created by a motor and pump assembly which siphons the oil from the cooking vessel. The pump pressures it through the filter material into the lid assembly means which is subsequently returned under pressure to the cooking vessel in filtered form. The introduction of the cooking oil into the filter canister from a pressure line coupled to a bottom orifice of the filter canister causes a compressing effect against the filter media that forces it to press upwardly against the retainer pad abutting a lower retainer and baffle means, or bottom wall, of the lid assembly, which bottom wall is concave. The lid assembly means includes the bottom wall, each being perforated in a proportion to the filter canister size. The side wall is spaced from an inside wall of the filter canister which forms a baffle space whereby the oil moving upward from the filter media and felt pad is moved under pressure into the annular baffle space for return through the outlet port back into the cooking vessel. A solid top wall of the lid means covers the open top of the filter canister in tight sealing relationship made possible by a gasket and mechanical locking means. The pressure line, also called the intermediate line, extends between the pump and the bottom orifice of the filter canister and has a length and internal diameter sized and proportioned to: the pump/motor size; the volume of the portion of the filter canister containing the filter; and, the intake and outlet dimensions of the system. The proportions are formulated so that the pressure line, the canister, and the annular baffle space are maintained at substantially equal back pressure, and to be substantially continuously filled with oil, so that the whole system from the siphon intake to the return tube is also substantially full under a substantially identical pressure during operation.
The inventive filtering system, method, and apparatus therefor, preferably utilize a raw cotton fiber as the filter medium in the filter canister, which is arranged to be easily removed and replaced.